Techniques for handling interrupts in a processing unit using interrupt request queues

ABSTRACT

A technique for handling interrupts in a data processing system includes receiving, at an interrupt presentation controller (IPC), an event notification message (ENM) that specifies an event target number and a number of bits to ignore. In response to a slot being available in an interrupt request queue, the IPC enqueues the ENM in the slot. In response to the ENM being dequeued from the interrupt request queue, the IPC determines a group of virtual processor threads that may be potentially interrupted based on the event target number and the number of bits to ignore specified in the ENM. The event target number identifies a specific virtual processor thread and the number of bits to ignore identifies the number of lower-order bits to ignore with respect to the specific virtual processor thread when determining a group of virtual processor threads that may be potentially interrupted.

BACKGROUND OF THE INVENTION

The present disclosure is generally directed to data processing systemsand, more specifically, to techniques for handling interrupts in aprocessing unit of a data processing system using interrupt requestqueues.

In data processing systems, an interrupt signal (interrupt) is generatedto indicate to a processor that an event requires attention. Dependingon a priority of an interrupt, a processor may respond by suspendingcurrent activities, saving state, and executing a function (i.e., aninterrupt handler) to service the event. For example, hardwareinterrupts may be generated by an input/output (I/O) device, e.g., diskdrive controller, a keyboard, a mouse, or other peripheral device. Incontrast, software interrupts may be caused either by an exceptioncondition in a processor or a special instruction in an instruction setarchitecture (ISA) that, when executed, causes an interrupt to begenerated. Following interrupt servicing, a processor resumes suspendedactivities.

An interrupt handler, also known as an interrupt service routine (ISR),is a callback function (e.g., implemented in firmware, an operatingsystem (OS), or a device driver) whose execution is triggered by aninterrupt. Interrupt handlers perform various interrupt dependentfunctions. For example, pressing a key on a computer keyboard or movinga computer mouse triggers interrupts that call respective interrupthandlers to read a key or a mouse position and copy associatedinformation into memory of a computer. In data processing systems, aninterrupt controller may be implemented to combine multiple interruptsources onto one or more processor exception lines, while facilitatingthe assignment of priority levels to different interrupts.

BRIEF SUMMARY

A technique for handling interrupts in a data processing system includesreceiving, at an interrupt presentation controller (IPC), an eventnotification message (ENM) that specifies an event target number and anumber of bits to ignore. In response to a slot being available in aninterrupt request queue, the IPC enqueues the ENM in the slot. Inresponse to the ENM being dequeued from the interrupt request queue, theIPC determines a group of virtual processor threads that may bepotentially interrupted based on the event target number and the numberof bits to ignore specified in the ENM. The event target numberidentifies a specific virtual processor thread and the number of bits toignore identifies the number of lower-order bits to ignore with respectto the specific virtual processor thread when determining a group ofvirtual processor threads that may be potentially interrupted.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a high-level block diagram of an exemplary data processingsystem in accordance with one embodiment of the present disclosure;

FIG. 2 is a more detailed block diagram of an exemplary processing unitin accordance with one embodiment of the present disclosure;

FIG. 3A is a diagram of exemplary fields of a conventional eventnotification message (ENM);

FIG. 3B is a diagram of exemplary fields of a conventional notificationrejection message (NRM);

FIG. 3C is a diagram of exemplary fields of a conventionalend-of-interrupt (EOI) message;

FIG. 4 is a block diagram of relevant components of an exemplaryconventional interrupt source controller (ISC);

FIG. 5 is a block diagram of relevant components of an exemplaryconventional interrupt presentation controller (IPC);

FIG. 6 is a flowchart of an exemplary process implemented by aconventional ISC to handle interrupts;

FIG. 7 is a flowchart of an exemplary process implemented by aconventional IPC to handle interrupts;

FIG. 8 is a flowchart of another exemplary process implemented by aconventional IPC to handle interrupts;

FIG. 9 is a flowchart of an exemplary process implemented by aconventional processor core to handle interrupts;

FIG. 10 is a flowchart of yet another exemplary process implemented by aconventional IPC to handle interrupts;

FIG. 11 is a flowchart of still another exemplary process implemented bya conventional IPC to handle interrupts;

FIG. 12 is a diagram of exemplary fields of an ENM that is configuredaccording to one embodiment of the present disclosure;

FIG. 13 is a graph that depicts a relationship between the number oflower-order bits to ignore and virtual processor (VP) threads that mayservice an associated interrupt according to an embodiment of thepresent disclosure;

FIG. 14 is a block diagram of relevant components of an exemplary ISCconfigured according to the present disclosure;

FIG. 15 is a block diagram of relevant components of an exemplary IPCconfigured according to the present disclosure;

FIG. 16A is a block diagram of relevant components of an exemplaryselector of the IPC of FIG. 15;

FIG. 16B is a block diagram of relevant components of an exemplarymessage queue of the IPC of FIG. 15;

FIG. 17 is a flowchart of an exemplary process implemented by an IPC,configured according to the present disclosure, to handle interrupts;

FIG. 18 is a flowchart of another exemplary process implemented by anIPC, configured according to the present disclosure, to handleinterrupts;

FIG. 19 is a flowchart of yet another exemplary process implemented byan IPC, configured according to the present disclosure, to handleinterrupts;

FIG. 20 is a flowchart of still another exemplary process implemented byan IPC, configured according to the present disclosure, to handleinterrupts; and

FIG. 21 is a flowchart of another exemplary process implemented by anIPC, configured according to the present disclosure, to handleinterrupts.

DETAILED DESCRIPTION

With reference now to the figures, wherein like reference numerals referto like and corresponding parts throughout, and in particular withreference to FIG. 1, there is illustrated a high level block diagramdepicting an exemplary data processing system 100 that implements one ormore interrupt presentation controllers (IPCs) and multiple interruptsource controllers (ISCs) configured in accordance with one or moreembodiments of the present disclosure. In the depicted embodiment, dataprocessing system 100 is a cache coherent symmetric multiprocessor (SMP)data processing system including multiple processing nodes 102 forprocessing data and instructions. Processing nodes 102 are coupled to asystem interconnect 110 for conveying address, data and controlinformation. System interconnect 110 may be implemented, for example, asa bused interconnect, a switched interconnect, or a hybrid interconnect.

In the depicted embodiment, each processing node 102 is realized as amulti-chip module (MCM) containing four processing units 104 a-104 d,each which may be realized as a respective integrated circuit. Theprocessing units 104 within each processing node 102 are coupled forcommunication to each other and system interconnect 110 by a localinterconnect 114, which, like system interconnect 110, may beimplemented, for example, with one or more buses and/or switches. Systeminterconnect 110 and local interconnects 114 together form a systemfabric.

Processing units 104 each include a memory controller (not shown)coupled to local interconnect 114 to provide an interface to arespective system memory 108. Data and instructions residing in systemmemories 108 can generally be accessed, cached, and modified by aprocessor core in any processing unit 104 of any processing node 102within data processing system 100. System memories 108 thus form thelowest level of memory storage in the distributed shared memory systemof data processing system 100. In alternative embodiments, one or morememory controllers (and system memories 108) can be coupled to systeminterconnect 110 rather than a local interconnect 114.

Those skilled in the art will appreciate that SMP data processing system100 of FIG. 1 can include many additional non-illustrated components,such as interconnect bridges, non-volatile storage, ports for connectionto networks or attached devices, etc. Because such additional componentsare not necessary for an understanding of the described embodiments,they are not illustrated in FIG. 1 or discussed further herein. Itshould also be understood, however, that the enhancements describedherein are applicable to data processing systems of diversearchitectures and are in no way limited to the generalized dataprocessing system architecture illustrated in FIG. 1.

Referring now to FIG. 2, a more detailed block diagram of an exemplaryprocessing unit 104, in accordance with one embodiment of the presentdisclosure, is depicted. In the depicted embodiment, each processingunit 104 is an integrated circuit including multiple processor cores 200for processing instructions and data. In a preferred embodiment, eachprocessor core 200 supports simultaneous multithreading (SMT) and thusis capable of independently executing multiple hardware threads ofexecution simultaneously.

Each processor core 200 is coupled to an interrupt presentationcontroller (IPC) 240 via memory I/O bus 210. IPC 240 includes aninterrupt context table (ICT) 242 that maintains various information forphysical processor (PP) threads. In one or more embodiments, IPC 240 iscoupled to each processor core 200 via respective exception lines 212,which are utilized to notify each processor core 200 of an associatedinterrupt for an assigned virtual processor thread. IPC 240 is alsocoupled to I/O controllers 220 via memory I/O bus 210. IPC 240 isconfigured to receive/send information via memory I/O bus 210 from/toI/O controllers 220 and/or processor cores 200.

Each I/O controller 220 includes a packet decoder 222 and an interruptsource controller (ISC) 224 that includes an event assignment table(EAT) 226, whose values may be set via software (e.g., by a hypervisor).Each I/O controller 220 is coupled to an I/O adapter 230 via an I/O bus214. A device or devices (not shown), e.g., disk drive, keyboard, mouse,may initiate interrupt generation by I/O controller 220 by signaling I/Oadapter 230 to send a packet to packet decoder 222 of I/O controller 220via I/O bus 214. EAT 226 includes information that I/O controller 220uses to create event notification messages (ENMs) that are sent to IPC240 via memory I/O bus 210. While only a single interrupt presentationcontroller is illustrated in FIG. 2, it should be appreciated that aprocessing unit configured according to the present disclosure mayinclude more than one interrupt presentation controller.

With reference now to FIG. 3A, a structure of an exemplary conventionalevent notification message (ENM) 302 is illustrated. ENM 302 includes an‘event target number’ field, an ‘event source number’ field, and an‘event priority’ field, as well as a field (not shown) that identifiesthe message as an event notification message. A value in the ‘eventtarget number’ field identifies a physical processor thread that is tobe interrupted to facilitate servicing of an associated interrupt by anassociated processor core. A value in the ‘event source number’ fieldidentifies a notification source that generated the interrupt. A valuein the ‘event priority’ field identifies a priority level of theinterrupt. ENM 302 is generated and issued by a conventional ISC 424(see FIG. 4) to indicate that a notification source (identified by the‘event source number’ field has generated the interrupt) and is receivedand processed by a conventional IPC 540 (see FIG. 5).

With reference now to FIG. 3B, a structure of an exemplary conventionalnotification rejection message (NRM) 304 is illustrated. NRM 304includes an ‘event source number’ field, as well as a field (not shown)that identifies the message as a notification rejection message. NRM 304is generated and issued by IPC 540 (see FIG. 5) and is received andprocessed by ISC 424 (see FIG. 4) to indicate, to ISC 424, that therequested interrupt was rejected and needs to be reissued.

With reference now to FIG. 3C, a structure of an exemplary conventionalend-of-interrupt (EOI) message 306 is illustrated. EOI message 306includes an ‘event source number’ field, as well as a field (not shown)that identifies the message as an EOI message. EOI message 304 isgenerated and issued by IPC 540 (see FIG. 5) and sent to ISC 424 (seeFIG. 4) to indicate, to ISC 424, that an interrupt requested by a deviceassociated with the event source number has been serviced.

With reference to FIG. 4, relevant components of conventional ISC 424are illustrated. It should be appreciated that ISC 424 is replaced byISC 224 in a processing unit configured according to the presentdisclosure. ISC 424 is included within an interrupt controller that alsoincludes a packet decoder 422 that is coupled to an I/O bus 414 (similarto I/O bus 214 of FIG. 2), a message decoder 404 (that is used to decodeEOI messages 306 and/or NRMs 304 received via memory I/O bus 410(similar to memory I/O bus 210 of FIG. 2)), an event assignment table(EAT) 426, and an interrupt message encoder 406 that utilizesappropriate information in EAT 426 to generate ENMs 302 for an interruptsource. Packet decoder 422 is configured to decode packets received viaI/O bus 414 and select a finite state machine (FSM) to process areceived packet based on an event source number of a source of thepacket. As is illustrated, ISC 424 includes an FSM for each row (i.e.,S-FSM 0 through S-FSM N) in EAT 426 that is configured to writeinformation into EAT 426 to facilitate building ENMs 302. It should beappreciated that the event source number illustrated in EAT 426 is not afield, but is only used to indicate a row number. For example, sourcenumber ‘0’ is assigned to row number ‘0’ of EAT 426, source number ‘1’is assigned to row number ‘1’ of EAT 426, etc. In EAT 426, each row hasan associated ‘event priority’ field and an ‘event target number’ field,whose values are utilized to populate corresponding fields in an ENM302, which is generated by interrupt message encoder 406 when aninterrupt is requested by an associated I/O device.

With reference to FIG. 5, relevant components of conventional IPC 540are illustrated. It should be appreciated that IPC 540 is replaced byIPC 240 in a processing unit configured according to the presentdisclosure. IPC 540 includes a message decoder 502, a memory mapped I/O(MMIO) unit 504, and a message encoder 506 coupled to memory I/O bus410. Processor cores communicate with IPC 540 via MMIO unit 504, usingMMIO loads and MMIO stores. IPC 540 receives messages from ISC 424 viamessage decoder 502. IPC 540 generates messages for ISC 424 via messageencoder 506. MMIO unit 504 issues a trigger EOI message 507 to messageencoder 506 to cause message encoder 506 to generate and send an EOImessage 306 on memory I/O bus 410 to ISC 424. Message decoder 502 iscoupled to selector 522, which is configured to select an FSM (i.e., oneof P-FSM 1 through P-FSM M) based on an event target number associatedwith a received ENM 302. FSMs of IPC 540 access interrupt context table(ICT) 542 to initiate generation of an exception to a physical processorthread executing on a processor core and to initiate generation of atrigger reject message 505 to message encoder 506, which generates anNRM 304 in response to trigger reject message 505.

It should be appreciated that the physical thread number illustrated ininterrupt context table (ICT) 542 is not a field, but is only used toindicate a row. For example, physical thread number ‘0’ is assigned torow number ‘0’ of ICT 542, physical thread number ‘1’ is assigned to rownumber ‘1’ of ICT 542, etc. In ICT 542, each row has an associated‘valid’ field, an ‘operating priority’ field, an ‘assigned’ field, an‘event source number’ field, and an ‘event priority’ field, whose valuesare set by FSMs and may be accessed to return values to a processor corein response to a MMIO load.

It should be appreciated that various blocks of the processes describedherein as being executed by an ISC (both conventionally and perembodiments of the present disclosure) may run simultaneously per row ofan associated EAT and that various blocks of the processes describedherein as being executed by an IPC (both conventionally and perembodiments of the present disclosure) may run simultaneously per row ofan associated ICT. As examples, at least portions of the variousprocesses may be performed by FSM logic associated with a given row ofan EAT and/or ICT or an engine may be implemented to perform the variousprocesses while sequencing through all rows of an EAT and/or ICT.

With reference to FIG. 6 an exemplary process 600 is illustrated that isimplemented by ISC 424 to handle interrupts. Process 600 may, forexample, be initiated in block 602 when ISC 424 receives input via I/Obus 414. Next, in decision block 604, ISC 424 determines whether thereceived input corresponds to an interrupt trigger (or interrupt triggerpulse). In response to the received input not being an interrupt triggercontrol loops on block 604. In response to the received input being aninterrupt trigger in block 604 control transfers to block 606. In block606, ISC 424 builds an ENM 302 based on associated information in EAT426. Next, in block 608, ISC 424 sends ENM 302 to IPC 540 via memory I/Obus 410.

Then, in decision block 610, ISC 424 determines whether a reject message(i.e., an NRM 304) has been received from IPC 540. For example, IPC 540may generate an NRM 304 in response to a physical processor thread thatis designated to be interrupted to service the interrupt having a higheroperating priority than an event priority of the interrupt. In responseto ISC 424 receiving an NRM 304 for ENM 302 in block 610 controltransfers to block 614, where process 600 waits a configurable timeperiod before returning control to block 606 where another ENM 302 isbuilt for the interrupt. In response to ISC 424 not receiving an NRM 304for ENM 302 in block 610 control transfers to decision block 612. Inblock 612, ISC 424 determines whether an EOI message 306 has beenreceived from IPC 540. In response to ISC 424 receiving an EOI message306 for ENM 302 in block 612 control returns to block 604. In responseto ISC 424 not receiving an EOI message 306 for ENM 302 in block 612control returns to block 610.

With reference to FIG. 7 an exemplary process 700 is illustrated that isimplemented by IPC 540 to handle interrupts. Process 700 maybe initiatedin block 702 when IPC 540 receives input via memory I/O bus 410. Next,in decision block 704, IPC 540 determines whether an ENM 302 wasreceived. In response to the received input not being an ENM 302 controlloops on block 704. In response to the received input being an ENM 302in block 704 control transfers to decision block 706. In block 706, IPC540 determines whether a valid bit for a row in ICT 542 that is assignedto an event target number (i.e., physical processor thread) specified inENM 302 is asserted (i.e., whether the specified physical processorthread is populated and operational, as specified by a valid field ofthe physical processor thread in ICT 542).

In response to the valid bit not being asserted in block 706 controltransfers to block 712, where error processing is initiated, and thenreturns to block 704. In response to the valid bit being asserted inblock 706 control transfers to decision block 708. In block 708, IPC 540determines whether a pending interrupt is already assigned to a physicalprocessor thread associated with the event source number (by examining avalue of an ‘assigned’ field of the specified physical processor threadin ICT 542). In response to a pending interrupt not already beingassigned to the specified physical processor thread in block 708 controltransfers to block 714. In block 714 IPC 540 asserts the ‘assigned’field, and sets the ‘event source number’ field, and the ‘eventpriority’ field for the specified physical processor thread based onvalues included in ENM 302. Following block 714 control returns to block704.

In response to a pending interrupt already being assigned to thephysical processor thread in block 708 control transfers to decisionblock 710. In block 710 IPC 540 determines whether an event priority ofa new interrupt, as specified in the ‘event priority’ field of ENM 302,is greater than an event priority of an already pending interrupt, asspecified in the ‘event priority’ field of the physical processor threadin ICT 542. In response to the event priority of the new interrupt notbeing greater than the event priority of the pending interrupt controltransfers from block 710 to block 716. In block 716 IPC 540 issues anNRM 304 to the event source number specified in ENM 302 (i.e., thesource associated with the new interrupt).

In response to the event priority of the new interrupt being greaterthan the event priority of the pending interrupt control transfers fromblock 710 to block 718. In block 718 IPC 540 issues an NRM 304 to theevent source number specified in ICT 542 (i.e., the source associatedwith the pending interrupt). Next, in block 720, IPC 540 modifies theevent source number and the event priority, as specified in ENM 302, forthe physical processor thread in ICT 542. Following block 720 controlreturns to block 704.

With reference to FIG. 8 an exemplary process 800 is illustrated that isimplemented by IPC 540 to assert/deassert exception lines based onassociated ‘assigned’ fields being asserted (indicating a pendinginterrupt) and an event priority for the pending interrupt being greaterthan or less or equal to an operating priority of a physical processorthread that is to be interrupted to facilitate servicing the interruptby an associated processor core. Process 800 may be periodicallyinitiated in block 802 by IPC 540 to determine whether exceptions linesto respective processor cores require assertion or de-assertion. Next,in decision block 804, IPC 540 determines whether an assigned field foreach row in ICT 542 is asserted (i.e., true), which indicates that aninterrupt is pending for an associated physical processor thread.

In response to an ‘assigned’ field not being asserted in a row of ICT542 control transfers from block 804 to block 810. In block 810 IPC 540deasserts an exception line associated with a row that was recentlyunassigned or maintains the exception line in a deasserted state for arow that is unassigned, but not recently unassigned. Following block 810control returns to block 804. In response to an assigned field beingasserted in a row of ICT 542 control transfers from block 804 todecision block 806. In block 806, IPC 540 determines whether an eventpriority of a pending interrupt is greater than an operating priority ofan associated physical processor thread.

In response to the event priority of a pending interrupt not beinggreater than an operating priority of an associated physical processorthread in block 806 control transfers to block 810, where associatedexception lines remain deasserted. In response to the event priority ofa pending interrupt being greater than an operating priority of anassociated physical processor thread in block 806 control transfers toblock 808, where associated exception lines are asserted. Followingblock 808 control returns to block 804.

With reference to FIG. 9, an exemplary process 900 that is implementedby a processor core to handle interrupts is illustrated. It should beappreciated that each processor core maintains an exception enable bit(e.g., in an internal register) for each associated exception line.Process 900 may be periodically executed by a processor core todetermine whether a physical processor thread should be interrupted tofacilitate executing, by the processor core, an interrupt handler toservice an interrupt. Process 900 is initiated in block 902 at whichpoint control transfers to decision block 904. In block 904 theprocessor core determine whether both an exception line and an exceptionenable bit are asserted. A processor core masks interrupts bydeasserting the exception enable bit.

In response to the exception line and/or the associated exception enablebit not being asserted control loops on block 904. In response to boththe exception line and the associated exception enable bit beingasserted control transfers from block 904 to block 906. In block 906 theprocessor core resets the exception enable bit (to prevent subsequentinterrupts from interrupting the current interrupt). Next, in block 908,the processor core changes control flow to an appropriate interrupthandler. Next, the processor core acknowledges the pending interrupt byissuing a MMIO load to IPC 540. Then, in block 910, the processor coreexecutes a program that is registered to handle interrupts from thesource (specified by a value in the ‘event source number’ field).

Next, in block 914, following completion of the program, the processorcore issues a MMIO store to IPC 540 to signal an EOI. Then, in block916, the processor core, resets the operating priority in the row in ICT542 that is associated with the physical processor thread to apre-interrupt value. Next, in block 918, the processor core atomicallyasserts the exception enable bit and returns control flow to a programthat was interrupted to service the interrupt. Following block 918control returns to block 904.

With reference to FIG. 10, an exemplary process 1000 that is implementedby IPC 540 to handle interrupts is illustrated. Process 1000 may beperiodically executed by IPC 540 to determine whether IPC 540 hasreceived a communication (e.g., MMIO load or a MMIO store) from aprocessor core with respect to a pending interrupt. Process 1000 isinitiated in block 1002 at which point control transfers to decisionblock 1004. In block 1004 IPC 540 determines whether a MMIO load hasbeen received at an interrupt acknowledge address.

In response to a MMIO load not being received at the interruptacknowledge address control loops on block 1004. In response to a MMIOload being received at the interrupt acknowledge address controltransfers to block 1006. In block 1006 IPC 540 atomically sets anoperating priority to the pending interrupt priority and resets theassigned field for the interrupt in ICT 542, and returns the pendinginterrupt source number as response data to the MMIO load. From block1006 control returns to block 1004.

With reference to FIG. 11, an exemplary process 1100 that is implementedby IPC 540, to handle changes in operating priority for a physicalthread, is illustrated. Process 1100 may be periodically executed by IPC540 to determine whether IPC 540 has received a communication (e.g., aMMIO load or a MMIO store) from a processor core with respect to apending interrupt. Process 1100 is initiated in block 1102 at whichpoint control transfers to decision block 1104. In block 1104 IPC 540determines whether a MMIO store has been received at an operatingpriority address.

In response to a MMIO store not being received at the operating priorityaddress control loops on block 1104. In response to a MMIO load beingreceived at the operating priority address control transfers from block1104 to block 1106. In block 1106, IPC 540 sets an operating priorityfor each row in ICT 542 per data associated with the MMIO store. Next,in decision block 1108, IPC 540 determines whether the operatingpriority is less than the pending priority for each row in ICT 542. Inresponse to the operating priority being less that a pending eventpriority control transfers from block 1108 to block 1104. In response tothe operating priority not being less than a pending event prioritycontrol transfers from block 1108 to block 1109 where the row assignedbit is reset along with the pending priority. Next, in block 1110, IPC540 issues a reject message to a notification source associated with thepending interrupt. From block 1110 control returns to block 1104.

According to an embodiment of the present disclosure, techniques areimplemented that may increase the number of threads that are availableto be interrupted by a given interrupt and, thus, increase thelikelihood of a given interrupt being serviced in a more timely manner.

With reference to FIG. 12, a structure of an exemplary eventnotification message (ENM) 1202, that is configured according to thepresent disclosure, is illustrated. ENM 1202 includes an ‘event targetnumber’ field, a ‘number of bits to ignore’ field, an ‘event sourcenumber’ field, and an ‘event priority’ field, as well as a field (notshown) that identifies the message as an event notification message. Avalue in the ‘event target number’ field identifies a virtual processor(VP) thread that is designated to be interrupted to facilitate servicingof an associated interrupt by an associated processor core. A value inthe ‘number of bits to ignore’ field specifies the number of lower-orderbits to ignore in the ‘event target number’ when determining which VPthreads may potentially be interrupted to service the interrupt. A valuein the ‘event source number’ field identifies a notification source thatgenerated the interrupt. A value in the ‘event priority’ fieldidentifies a priority level of the interrupt.

ENM 1202 is generated by an interrupt source controller (ISC) 224 thatis configured according to the present disclosure (see FIG. 14) andissued to an interrupt presentation controller (IPC) 240 that isconfigured according to the present disclosure (see FIG. 15) to indicatethat a notification source, identified by the ‘event source number’field, has generated the interrupt. It should be appreciated that ENM1202 is similar to ENM 302, with some exceptions being that ENM 1202includes an additional field that specifies a ‘number of bits to ignore’that is used when selecting a virtual processor (VP) thread to interruptand that the ‘event target value’ field identifies a virtual processorthread, as contrasted with a physical processor thread.

For example, assuming that sixteen VP threads are implemented (i.e., VPthreads 0000 through 1111) the number of VP threads that may beconsidered for interruption may be specified as a single VP thread orall sixteen VP threads depending on a value specified in the ‘number ofbits to ignore’ field. As one example, assuming that VP thread eight,i.e., ‘1000’, is specified in the ‘event target number’ field and thatthree is specified in the ‘number of bits to ignore’ field, then eightVP threads (i.e., ‘1000’ through ‘1111’) may be considered forinterruption to service an associated interrupt. As another example,assuming that VP thread eight, i.e., ‘1000’, is specified in the ‘eventtarget number’ field and that zero is specified in the ‘number of bitsto ignore’ field, then only VP thread eight (i.e., ‘1000’) may beconsidered for interruption to service an associated interrupt.

With reference to FIG. 13, a graph 1300 is illustrated that depicts arelationship between the number of (lower-order) bits to ignore andvirtual processor (VP) threads that may potentially service anassociated interrupt for a data processing system the deploys up tosixteen VP threads, according to an embodiment of the presentdisclosure. It should be appreciated that the disclosed techniques areapplicable to data processing systems that deploy more or less thansixteen VP threads. As is illustrated in graph 1300, when the ‘number ofbits to ignore’ is four all sixteen VP threads are potentially availableto service an associated interrupt. When the ‘number of bits to ignore’is three, eight VP threads are potentially available to service anassociated interrupt. When the ‘number of bits to ignore’ is two, fourVP threads are potentially available to service an associated interrupt.When the ‘number of bits to ignore’ is one, two VP threads arepotentially available to service an associated interrupt. When the‘number of bits to ignore’ is zero, one VP thread is potentiallyavailable to service an associated interrupt. In general, where the‘number of bits to ignore’ is ‘n’ bits, a specified virtual processorthread and 2^(n)−1 other virtual processor threads may be potentiallyinterrupted.

With reference to FIG. 14, relevant components of ISC 224 of FIG. 2,which is configured according to the present disclosure, are furtherillustrated. As previously mentioned, interrupt controller 220 includespacket decoder 222, which is coupled to I/O bus 214, and ISC 224. ISC224 includes a message decoder 1404 (that is used to decode conventionalEOI messages 306 and/or NRMs 304 received via memory I/O bus 210), eventassignment table (EAT) 226, and an interrupt message encoder 1406 thatutilizes appropriate information in EAT 226 to generate ENMs 1202 for anotification source. Packet decoder 222 is configured to decode packetsreceived via I/O bus 214 and select a finite state machine (FSM) toprocess the received packet based on an event source number for a sourceof the packet.

As is illustrated, ISC 224 includes an FSM for each row (i.e., S-FSM 0through S-FSM N) in EAT 226 that is configured to maintain informationin EAT 226 to facilitate building ENMs 1202. It should be appreciatedthat the event source number illustrated in EAT 226 is not a field, butis only used to indicate a row number. For example, source number ‘0’ isassigned to row number ‘0’ of EAT 226, source number ‘1’ is assigned torow number ‘1’ of EAT 226, etc. In EAT 226, each row has an associated‘event priority’ field, an ‘event target number’ field, and a ‘number ofbits to ignore’ field, whose values are utilized to populatecorresponding fields in an ENM 1202, which is generated by interruptmessage encoder 1406 when an interrupt is requested by an associated I/Odevice.

With reference to FIG. 15, relevant components of IPC 240 are furtherillustrated. IPC 240 includes a message queue 1501, a memory queue(MEMQ) 1503, a memory mapped I/O (MMIO) unit 1504, and a message encoder1506 coupled to memory I/O bus 210. Processor cores 200 communicate withIPC 240 via MMIO unit 1504, using MMIO loads and MMIO stores. IPC 240receives messages from ISC 224 via message queue 1501, which is coupledto message decoder 1502. IPC 240 generates messages for ISC 224 viamessage encoder 1506. MMIO unit 1504 issues a trigger EOI message 1507to message encoder 1506 to cause message encoder 1506 to generate andsend an EOI message 306 on memory I/O bus 210 to ISC 224. Messagedecoder 1502 receives enqueued ENMs 1202 from message queue 1501.Message decoder 1502 is coupled to selector 1508, which is configured toselect an FSM (i.e., one of P-FSM 1 through P-FSM M) for packetprocessing based on an event target number associated with a receivedENM 1202. FSMs of IPC 240 access interrupt context table (ICT) 242 toinitiate generation of an exception to a physical thread executing on aprocessor core 200 and to generate a trigger reject message 1505 tomessage encoder 1506, which generates an NRM 304 in response to triggerreject message 1505.

It should be appreciated that the physical processor thread numberillustrated in ICT 242 is not a field, but is only used to indicate arow. For example, physical (processor) thread number ‘0’ is assigned torow number ‘0’ of ICT 242, physical thread number ‘1’ is assigned to rownumber ‘1’ of ICT 242, etc. In ICT 242, each row has an associated‘valid’ field, virtual processor number (‘VP #’) field, an ‘operatingpriority’ field, an ‘assigned’ field, an ‘event source number’ field,and an ‘event priority’ field, whose values may be retrieved by aprocessor core using a MMIO load in response to an exception line beingasserted by IPC 240. The ‘valid’ field indicates whether a processor isinstalled and powered on and whether a VP is dispatched and operating onan associated physical processor thread. The ‘VP #’ field specifies anumber of the VP that is dispatched on the associated physical processorthread. The ‘operating priority’ field specifies a priority level of aprogram currently running on the associated physical processor thread.

With reference to FIG. 16A, relevant components of selector 1508 of IPC240 of FIG. 15 are further illustrated, according to one embodiment ofthe present disclosure. As is depicted, selector 1508 includecomparators (CMP 0 through CMP M), i.e., one for each row in ICT 242,that compare an ‘event target number’ and ‘number of bits to ignore’provided in ENM 1202 and ‘valid’ and ‘VP #’ values stored in respectiverows of ICT 242. Outputs of the comparators are provided to a ‘no hits’unit 1602 which determines whether any VP threads are available to beinterrupted. In the event zero VP threads are available to beinterrupted, ‘no hits’ unit 1602 issues trigger reject message 1505 tomessage encoder 1506 (see FIG. 15). In the event more than one VP threadis available to be interrupted, ‘secondary selection’ unit 1604determines which VP thread should be interrupted and issues anappropriate interrupt trigger to trigger an interrupt on an associatedphysical processor thread.

‘Secondary selection’ unit 1604 may implement various secondaryselection criteria in determining which available VP thread to selectfor interruption. For example, ‘secondary selection’ unit 1604 mayselect a VP thread to interrupt based on ‘event priority’ relative to‘operating priority’, least recently used (LRU), and/or random, etc. Itshould be appreciated that the various selection criteria may beimplemented in series to select a single VP thread when multiple VPthreads are still available after a given selection process.

With reference to FIG. 16B, relevant components of message queue 1501 ofIPC 240 of FIG. 15 are further illustrated, according to one embodimentof the present disclosure. As is depicted, message queue 1501 includes acontroller 1650, a head-of-line-queue (HOLQ) 1654, and anend-of-line-queue (EOLQ) 1652. Controller 1650 is configured to controlaccess to HOLQ 1654, EOLQ 1652, and MEMQ 1503. MEMQ 1503 may be, forexample, located in system memory 108 or another memory. In general, thecombination of HOLQ 1654, EOLQ 1652, and MEMQ 1503 function as aninterrupt request queue for IPC 240. As is discussed in further detailbelow (see FIGS. 17-20), a ENM 1202 received by IPC 240 may be enqueuedat one time or another in HOLQ 1654; HOLQ 1654 and EOLQ 1652; or HOLQ1654, EOLQ 1652, and MEMQ 1503 prior to being processed by messagedecoder 1502.

With reference to FIG. 17 an exemplary process 1700 is illustrated thatis implemented by IPC 240 to handle interrupts. It should be appreciatedthat IPC 240 handles event notification messages differently from howIPC 540 handles event notification messages (see FIG. 7). Process 1700is initiated in block 1702 when IPC 240 receives input via memory I/Obus 210. Next, in decision block 1704, IPC 240 determines whether anevent notification message (ENM) 1202 was received. It should beappreciated that ISC 224 operates similarly to ISC 424 (see FIG. 6) andthat ENM 1202 is built by ISC 224 in a manner that is similar to themanner described for ISC 424 to build ENM 302, with the exception thatENM 1202 is built to include an additional field (i.e., a ‘number ofbits to ignore’ field) and the ‘event target number’ field provides avirtual processor thread number, as contrasted with a physical processorthread number.

In response to the received input not corresponding to an ENM 1202control loops on block 1704. In response to the received inputcorresponding to an ENM 1202 in block 1704 control transfers to decisionblock 1706. In block 1706, IPC 240 (or more specifically controller1650) determines whether there is a free slot in HOLQ 1654 and whetherEOLQ 1652 is empty. In response to there being a free slot in HOLQ 1654and EOLQ 1652 being empty control transfers from block 1706 to block1708. In block 1708, IPC 240 enqueues the received ENM 1202 in HOLQ1654. From block 1708 control then returns to block 1704. In response tothere not being a free slot in HOLQ 1654 or EOLQ 1652 not being emptycontrol transfers from block 1706 to decision block 1710. In block 1710IPC 240 determines whether there is a free slot in EOLQ 1652. Inresponse to there being a free slot in EOLQ 1652 in block 1710 controltransfers to block 1712, where IPC 240 enqueues the received ENM 1202 inEOLQ 1652. From block 1712 control returns to block 1704. In response tothere not being a free slot in EOLQ 1652 in block 1710 control transfersto block 1714, where IPC 240 sends a reject message (i.e., NRM 304) toISC 242. From block 1714 control then returns to block 1704.

With reference to FIG. 18 an exemplary process 1800 is illustrated thatis implemented by IPC 240 to handle interrupts. Process 1800 isinitiated in block 1802 when, for example, IPC 240 completes processingan ENM 1202. Next, in decision block 1804, IPC 240 determines whetherHOLQ 1654 has an enqueued ENM 1202. In response to HOLQ 1654 not havingan enqueued ENM 1202 control loops on block 1804. In response to HOLQ1654 having an enqueued ENM 1202 in block 1804 control transfers toblock 1805. In block 1805, IPC 240 decodes the oldest ENM 1202 in HOLQ1654 and marks the slot previously occupied by the oldest ENM 1202 inHOLQ 1654 as free.

Next, in block 1806, IPC 240 compares the ‘event target number’ from ENM1202 with all valid VP numbers, ignoring the number of lower-order bitsspecified (in the ‘number of bits to ignore’ field) by ENM 1202. Then,in decision block 1808, IPC 240 determines whether a hit occurred for atleast one VP thread. In response to no hits (i.e., no VP threads beingavailable to be interrupted due to no VP thread being valid that meetsthe VP selection criteria (i.e., specified in the ‘event target number’field and the ‘number of bits to ignore’ field)) occurring in block 1808control transfers to block 1810, where IPC 240 issues a reject message(i.e., NRM 304) to a notification source specified by the ‘event sourcenumber’ field in ENM 1202. It should be appreciated that varioustechniques may be employed to ensure that an associated interrupt thatis rejected is eventually serviced. Following block 1810 control returnsto block 1804. In response to at least one hit occurring in block 1808control transfers to decision block 1812, where IPC 240 determineswhether there are any hits that do not have a pending interrupt alreadyassigned.

In response to IPC 240 determining that there is at least one hit thatdoes not already have a pending interrupt assigned in block 1812 controltransfers to block 1816. In block 1816, IPC 240 selects a row in ICT 242to trigger an interrupt. Next, in block 1818, IPC 240 sets an ‘assigned’field, a ‘source number’ field, and an ‘event priority’ field of theselected row per ENM 1202. Following block 1818 control returns to block1804. In response to IPC 240 determining that there are no hits that donot already have a pending interrupt assigned in block 1812 controltransfers to decision block 1814. In block 1814, IPC 240 determineswhether an interrupt priority (i.e., the event priority) of ENM 1202 isgreater than an operating priority of any row with a hit that has apending interrupt.

In response to the interrupt priority not being greater than anoperating priority of any row with a hit that has a pending interruptcontrol transfers from block 1814 to block 1810. In response to theinterrupt priority being greater than an operating priority of at leastone row with a hit that has a pending interrupt control transfers fromblock 1814 to block 1820. In block 1820, IPC 240 selects a row in ICT242 to trigger an interrupt. Next, in block 1822, IPC 240 issues areject message to an assigned notification source of the selected row inICT 242. Then, in block 1818, IPC 240 sets an ‘assigned’ field, a‘source number’ field, and an ‘event priority’ field of the selected rowin ICT 224 per ENM 1202. Following block 1818 control returns to block1804.

With reference to FIG. 19 an exemplary process 1900 is illustrated thatis implemented by IPC 240 to handle interrupts. Process 1900 isinitiated in block 1902 when, for example, IPC 240 (or more specificallycontroller 1650) receives an ENM 1202 via memory I/O bus 210. Next, indecision block 1904, IPC 240 determines whether there are less than ‘N’free slots in EOLQ 1652. In response to there not being less than ‘N’free slots in EOLQ 1652 control loops on block 1904. In response threebeing less than ‘N’ free slots in EOLQ 1652 in block 1904 controltransfers to decision block 1906. In block 1906, IPC 240 determineswhether there is a free slot (or slots) in MEMQ 1503. In response tothere not being a free slot (or slots) in MEMQ 1503 control loops onblock 1906. In response there being a free slot (or slots) in MEMQ 1503control transfers from block 1906 to block 1908. In block 1908, IPC 240writes the oldest ENM 1202 (or oldest ENMs 1202) in EOLQ 1652 to MEMQ1503 to free-up slots in EOLQ 1652. From block 1908 control then returnsto block 1904.

With reference to FIG. 20 an exemplary process 2000 is illustrated thatis implemented by IPC 240 to handle interrupts. Process 2000 isinitiated in block 2002 when, for example, IPC 240 completes servicingan ENM 1202. Next, in decision block 2004, IPC 240 determines whetherthere is a free slot (or slots) in HOLQ 1654. In response there notbeing a free slot in HOLQ 1654 control loops on block 2004. In responsethere being a free slot in HOLQ 1654 in block 2004 control transfers todecision block 2006. In block 2006, IPC 240 (or more specificallycontroller 1650) determines whether there is an ENM 1202 (or ENMs 1202)enqueued in MEMQ 1503. In response to there being an ENM 1202 enqueuedin MEMQ 1503 control transfers from block 2006 to block 2008. In block2008, IPC 240 moves the oldest ENM 1202 in MEMQ 1503 to a youngest slotin HOLQ 1654 and marks a slot previously associated with the oldest ENM1202 in MEMQ 1503 as free. From block 2008 control then returns to block2004.

In response to there not being an ENM 1202 enqueued in MEMQ 1503 inblock 2006, control transfers to decision block 2010. In block 2010, IPC240 determines whether there is an ENM 1202 enqueued in EOLQ 1652. Inresponse to there being an ENM 1202 enqueued in EOLQ 1652 in block 2010control transfers to block 2012. In block 2012, IPC 240 moves the oldestENM 1202 in EOLQ 1652 to a youngest free slot in HOLQ 1654 and marks theslot associated with the moved ENM 1202 in EOLQ 1652 as free. From block2012 control returns to block 2004. In response to there not being amessage enqueued in EOLQ 1652 in block 2010 control transfers directlyto block 2004.

With reference to FIG. 21 an exemplary process 2100 is illustrated thatis implemented by IPC 240 to handle certain MMIO stores received from aprocessor core. For example, a processor core 200 may issue a MMIO storeto IPC 242 to invalidate all associated VPs. Process 2100 is initiatedin block 2102 when, for example, IPC 240 receives a MMIO store from agiven processor core 200. Next, in decision block 2104, IPC 240determines whether the MMIO store is directed to deasserting a valid bitin one or more rows in ICT 242. In response to the received MMIO storenot being directed to deasserting a valid bit in one or more rows in ICT242 control loops on block 2104. In response to the received MMIO storebeing directed to deasserting a valid bit in one or more rows in ICT 242control transfers from block 2104 to decision block 2106.

In decision block 2106, IPC 240 determines whether the assigned bit isasserted in a row, i.e., whether an interrupt is pending for a row whosevalid bit is to be deasserted. In response to the assigned bit beingasserted for a row control transfers from block 2106 to block 2108. Inblock 2108 IPC 240 issues a reject message to a notification source(specified by a value in an ‘event source number’ field of a row in ICT242) associated with the row to which the valid bit is to be deasserted.Next, in block 2110 IPC 240 atomically deasserts values in the‘assigned’ field and the ‘valid’ field associated with the row (toindicate that an interrupt is no longer pending for the row or rows andthat the row or rows do not have a valid VP). Following block 2110control returns to block 2104. In response to the assigned bit not beingasserted for a row or rows in block 2106 control transfers to block2112. In block 2112 IPC 240 deasserts the valid bit for the row or rows.Following block 2112 control returns to block 2104.

Accordingly, techniques have been disclosed herein that generallyimprove the servicing of interrupts. It should be appreciated thataspects of the present disclosure may be implemented in a designstructure that is tangibly embodied in a computer-readable storagedevice for designing, manufacturing, or testing an integrated circuit.

In the flow charts above, the methods depicted in the figures may beembodied in a computer-readable medium as one or more design files. Insome implementations, certain steps of the methods may be combined,performed simultaneously or in a different order, or perhaps omitted,without deviating from the spirit and scope of the invention. Thus,while the method steps are described and illustrated in a particularsequence, use of a specific sequence of steps is not meant to imply anylimitations on the invention. Changes may be made with regards to thesequence of steps without departing from the spirit or scope of thepresent invention. Use of a particular sequence is therefore, not to betaken in a limiting sense, and the scope of the present invention isdefined only by the appended claims.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment or an embodiment combining softwareand hardware aspects that may all generally be referred to herein as a“circuit,” “module” or “system.”

Any combination of one or more computer-readable medium(s) may beutilized. The computer-readable medium may be a computer-readable signalmedium or a computer-readable storage medium. A computer-readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing, butdoes not include a computer-readable signal medium. More specificexamples (a non-exhaustive list) of the computer-readable storage mediumwould include the following: a portable computer diskette, a hard disk,a random access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), a portablecompact disc read-only memory (CD-ROM), an optical storage device, amagnetic storage device, or any suitable combination of the foregoing.In the context of this document, a computer-readable storage medium maybe any tangible storage medium that can contain, or store a program foruse by or in connection with an instruction execution system, apparatus,or device.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular system,device or component thereof to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodimentsdisclosed for carrying out this invention, but that the invention willinclude all embodiments falling within the scope of the appended claims.Moreover, the use of the terms first, second, etc. do not denote anyorder or importance, but rather the terms first, second, etc. are usedto distinguish one element from another.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiments were chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A processing unit for a multithreaded dataprocessing system, the processing unit comprising: an interrupt sourcecontroller (ISC); and an interrupt presentation controller (IPC) coupledto the ISC, wherein the IPC is configured to: receive an eventnotification message (ENM), wherein the ENM specifies an event targetnumber and a number of bits to ignore; in response to a slot beingavailable in an interrupt request queue of the data processing system,enqueue the ENM in the slot; and in response to the ENM being dequeuedfrom the interrupt request queue, determine a group of virtual processorthreads that may be potentially interrupted based on the event targetnumber and the number of bits to ignore specified in the ENM, whereinthe event target number identifies a specific virtual processor threadand the number of bits to ignore identifies a positive, integer numberof lower-order bits to ignore with respect to the specific virtualprocessor thread when determining a group of virtual processor threadsthat may be potentially interrupted.
 2. The processing unit of claim 1,wherein the IPC is further configured to: determine whether one or morevirtual processor threads within the group of virtual processor threadsare dispatched and operating on an associated physical processor; and inresponse to no virtual processor thread within the group of virtualprocessor threads being dispatched and operating on an associatedphysical processor, issue a reject message to a notification sourcespecified by an event source number in the ENM.
 3. The processing unitof claim 1, wherein the IPC is further configured to: determine whethermultiple virtual processor threads within the group of virtual processorthreads are dispatched and operating on an associated physicalprocessor; and in response to the multiple virtual processor threadswithin the group of virtual processor threads being dispatched andoperating on an associated physical processor, select one of themultiple virtual processor threads to interrupt that does not alreadyhave a pending interrupt.
 4. The processing unit of claim 3, wherein theIPC is further configured to: in response to more than one of themultiple virtual processor threads not already having a pendinginterrupt, select one of the multiple virtual processor threads tointerrupt that does not already have a pending interrupt based onsecondary selection criteria.
 5. The processing unit of claim 4, whereinthe secondary selection criteria includes one or more of an eventpriority of the ENM relative to an operating priority for each of themultiple virtual processor threads, a least recently used (LRU) one ofthe multiple virtual processor threads, and a random one of the multiplevirtual processor threads.
 6. The processing unit of claim 1, whereinthe number of bits to ignore is not equal to zero and the IPC is furtherconfigured to: determine whether multiple virtual processor threadswithin the group of virtual processor threads are dispatched andoperating on an associated physical processor; in response to themultiple virtual processor threads within the group of virtual processorthreads being dispatched and operating on an associated physicalprocessor, determine whether all of the multiple processor threads havepending interrupts; in response to determining that all of the multipleprocessor threads have pending interrupts, determine whether an eventpriority of the ENM is greater than an operating priority of any of themultiple virtual processor threads; and in response to determining thatthe event priority of the ENM is not greater than the operating priorityof any of the multiple virtual processor threads, issue a reject messageto a notification source specified by an event source number in the ENM.7. The processing unit of claim 1, wherein the IPC is further configuredto: in response to a slot not being available in the interrupt requestqueue, issue a reject message to a notification source specified by anevent source number in the ENM.
 8. A design structure tangibly embodiedin a computer-readable storage device for designing, manufacturing, ortesting an integrated circuit, the design structure comprising: aninterrupt source controller (ISC); and an interrupt presentationcontroller (IPC) coupled to the ISC, wherein the IPC is configured to:receive an event notification message (ENM), wherein the ENM specifiesan event target number and a number of bits to ignore; in response to aslot being available in an interrupt request queue of a multithreadeddata processing system that includes the ISC and the IPC, enqueue theENM in the slot; and in response to the ENM being dequeued from theinterrupt request queue, determine a group of virtual processor threadsthat may be potentially interrupted based on the event target number andthe number of bits to ignore specified in the ENM, wherein the eventtarget number identifies a specific virtual processor thread and thenumber of bits to ignore identifies a positive, integer number oflower-order bits to ignore with respect to the specific virtualprocessor thread when determining a group of virtual processor threadsthat may be potentially interrupted.
 9. The design structure of claim 8,wherein the IPC is further configured to: in response to a slot notbeing available in the interrupt request queue, issue a reject messageto a notification source specified by an event source number in the ENM.